In field bus systems heretofore, conventional clock sources are used for the clock supply for data transmission. For field bus systems having rapid binary data transmission it is difficult to maintain the tolerance limits for interfering electromagnetic radiation. Avoidance of analog signal forms requires expensive parts in the field bus system. Interfering radiation is reduced by the use of spread spectrum technology, which is based on varying the frequency of a signal and thus obtaining a data or clock signal with a varying bit length.
The use of spread spectrum clock signals in field bus devices is known from U.S. Pat. No. 7,010,621 B2 for at least partially limiting emissions of interfering electromagnetic radiation originating from a local oscillator. However, the linkage of adjacent field bus devices by returning spread spectrum clock signals to the local field bus device is not provided.
A network controller is known from U.S. 2002/0112070 A1 which directs messages between a plurality of remote users of a field bus. The bit rate of the messages may be modified by the network controller without using clock signals.